// My-own-MVC-framework/src/test/src/main/java/com/example/test/arithmeticCalculator.java

public static int calculate(PositiveNumber operand1, String operator, PositiveNumber operand2) {
        return arithmeticOperators.stream()
                .filter(arithmeticOperator -> arithmeticOperator.supports(operator))
                .map(arithmeticOperator -> arithmeticOperator.calculate(operand1, operand2)) // << issue
                .findFirst()
                .orElseThrow(()-> new IllegalArgumentException("올바른 연산이 아닙니다"));
    }

// My-own-MVC-framework/src/test/src/main/java/com/example/test/arithmeticCalculator.java

public static int calculate(int operand1, String operator, int operand2) {
        ArithmeticOperator arithmeticOperator = Arrays.stream(values())
                .filter(v -> v.operator.equals(operator))
                .findFirst()
                .orElseThrow(() -> new IllegalArgumentException("올바른 연산이 아닙니다"));

        return arithmeticOperator.arithmeticCalculate(operand1, operand2);
    }

@WebServlet("/")
public class DispatcherServlet extends HttpServlet {
    ...
    @Override
    public void service(HttpServletRequest req, HttpServletResponse res){
    ...
    Controller handler = requestMappingHandlerMapping.findHandler(req.getRequestURI());

public class RequestMappingHandlerMapping {
    // key : users/, value : userController
    private Map<String, Controller> mappings = new HashMap<>();

    public void init(){
        mappings.put("/", new HomeController());
        mappings.put("/users", new UserListController());
    }

    public Controller findHandler(String uriPath){
        return mappings.get(uriPath);
    }
}

public class HomeController implements Controller{
    @Override
    public String handleRequest(HttpServletRequest request, HttpServletResponse response) throws Exception {
        return "home.jsp";
    }
}

@WebServlet("/")
public class DispatcherServlet extends HttpServlet {
    ...
    @Override
    public void service(HttpServletRequest req, HttpServletResponse res){
    ...
        View view = viewResolver.resolveViewname(ModelAndView, getViewName());
        view.render(ModelAndView.getModel(), req, res);

// CustomWebApplicationServer
public class CustomWebApplicationServer {

    private final int port;

    private static final Logger logger = LoggerFactory.getLogger(CustomWebApplicationServer.class);
    public CustomWebApplicationServer(int port) {
        this.port = port;
    }

    public void start() throws IOException {
      while((clientSocket = serverSocket.accept()) != null){
                      logger.info("[CustomWebApplicationServer] client connected.");
                      new Thread(new ClientRequestHandler(clientSocket)).start(); // [1]

// ClientRequestHandler
public class ClientRequestHandler implements Runnable {

    @Override
    public void run() {
//      [2]
   }

// annonymous Class
public void create(User user) throws SQLException {

        JdbcTemplate jdbcTemplate = new JdbcTemplate();
        String sql = "INSERT INTO USERS VALUES (?,?,?,?)";
        jdbcTemplate.executeUpdate(user, sql, new PreparedStatementSetter() {
            @Override
            public void Setter(PreparedStatement pstamt) throws SQLException {
                pstamt.setString(1, user.getUserid());
                pstamt.setString(2, user.getPassword());
                pstamt.setString(3, user.getName());
                pstamt.setString(4, user.getEmail());
            }
        });
    }

// lambda
public void create(User user) throws SQLException {

        JdbcTemplate jdbcTemplate = new JdbcTemplate();
        String sql = "INSERT INTO USERS VALUES (?,?,?,?)";
        jdbcTemplate.executeUpdate(user, sql, pstamt -> {
            pstamt.setString(1, user.getUserid());
            pstamt.setString(2, user.getPassword());
            pstamt.setString(3, user.getName());
            pstamt.setString(4, user.getEmail());
        });
    }

private Set<Class<?>> getTypesAnnotatedWith(List<Class<? extends Annotation>> annotations) {
        Reflections reflections = new Reflections("com.example");

        Set<Class<?>> beans = new HashSet<>();
        annotations.forEach(annotation -> beans.addAll(reflections.getTypesAnnotatedWith(annotation)));
        
        return beans;
    }
// annotationd의 List로 들어온 인자들을 하나씩 꺼내 reflection의 prefix에 존재하는 클래스를 모두 beans에 추가해준다

// CustomWebApplicationServer
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;

public class CustomWebApplicationServer {
  private final ExecutorService executorService = Executors.newFixedThreadPool(10); // Thread 10개를 운용하는 Pool

  //   new Thread(new ClientRequestHandler(clientSocket)).start();
  executorService.execute(new ClientRequestHandler(clientSocket));
}

@Override
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        log.info("service");
        int operand1 = Integer.parseInt(request.getParameter("operand1"));
        String operator = request.getParameter("operator");
        int operand2 = Integer.parseInt(request.getParameter("operand2"));

        int result = Calculator.calculate(new PositiveNumber(operand1),operator ,new PositiveNumber(operand2));

        PrintWriter writer = response.getWriter();
        writer.println(result);
    }

public class Counter implements Runnable{

    @Override
    public void run() {
        synchronized (this) { // 동기화 사용
            this.increment();
            System.out.println("value for Thread After increment " 
                        + Thread.currentThread().getName() + " " + this.getValue()); // 1
            this.decrement();
            System.out.println("value for Thread at last "
                        + Thread.currentThread().getName() + " " + this.getValue()); // 0
        }
    }